Mass fish deaths caused by 'mismanagement'

The NSW government has been forced to defend its record following a new report pointing to mismanagement as the cause of mass fish deaths in the Murray-Darling.

Up to a million fish died in the Darling River at Menindee early last week when a cool change swept the region, killing off an existing algal bloom and depleting oxygen which worsened water quality.

The NSW and federal governments have been under pressure by scientists who say mismanagement of water is to blame.

A paper released by the Australia Institute says the drought may have been the catalyst for the critical ecological incident but the blame lays with state and federal governments and water agencies for mismanagement of the river.

"To blame the fish kill on the drought is a cop-out, it is because water releases were made from the Lakes when this simply shouldn't have happened," Australia Institute senior researcher Maryanne Slattery said in a statement.

The report, A fish kill QandA, says the lakes were possibly drained to justify the Menindee Lakes Water Saving and other projects.

But NSW Regional Water Minister Niall Blair dismissed the claim, insisting there had been many releases over the years and many people were responsible.

"Hindsight is fantastic," Mr Blair told AAP on Saturday afternoon.

When the water was ordered and released, modelling showed it would be replaced by inflows, he said. Decision-makers would have factored-in this information.

"We are now debating whether they were right or wrong ... this is the lowest inflows we've ever seen," he said, adding the drought had affected the situation.

The report says the Murray-Darling Basin Authority is partly responsible as it co-ordinated the management of the lakes for most of the time during the releases.

In response, the MDBA released a statement saying is was "confident the Menindee Lakes have been operated using the best information available" and the report was a "narrow view of operational issues".

The report says claims by the NSW government that the incident was "under the control of Canberra" are false as releases by the MDMA cannot be made without approval by the Basin Officials Committee, which is directed by the state governments.